Olympus E-M1 has a
16.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor and features TruePIC VII processor. On the other hand, Sony A7S III has a
12.0MP Full frame (35.6 x 23.8 mm ) sized BSI-CMOS sensor and features Bionz XR processor.
Below you can see the E-M1 and A7S III sensor size comparison.
Sensor Size and Resolution Comparison image of Olympus E-M1 and Sony A7S III Cameras
As seen above, Sony A7S III has a 3.8x Larger sensor area than Olympus E-M1. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.
DxOMark Sensor Scores
DxOMark is a benchmark that scientifically assesses image quality of camera sensors. It scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Olympus E-M1 and Sony A7S III sensors have been tested by DxO and the results show that A7S III has a better overall score of 85, 12 points higher compared to E-M1's score of 73.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Olympus E-M1
73
23.0 bits
12.7 Evs
757 ISO
Sony A7S III
85
24.2 bits
13.4 Evs
3900 ISO
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Olympus E-M1
or the
Sony A7S III ,
including hyperfocal distance.
One thing to watch when comparing these two: they have different sensor sizes
(Four Thirds versus Full frame),
so compare them at the same framing rather than the same focal length.
Put the same focal length on the smaller sensor and it will show less depth of
field, not more, because it also crops tighter. The calculator shows the
full frame equivalent focal length for each body so you can match the framing.
